Atmospheric fog, day, night and the stars.
 
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  1. #1
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    Atmospheric fog, day, night and the stars.

    This might be a question with an obvious answer.

    Ok, so during the day light from the sun bounces off the air in the atmosphere and into our eyes. because the atmosphere isn't solid it's transparent, but as layers of it build up (IE as we see further away) more of the air is visible, creating a fog.

    So at night, we can see the stars because of the lack of light bouncing off the atmosphere, correct?

    Now, does that mean an atmosphereic fog to create depth at night would be incorrect?

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    well.. I don't know about the theory, but I remember being at the top of an astronomical observatory at night, looking at the surrounding mountains and telling myself :" so atmospheric perspective works at night too."

    Yep, mountains in the distance were lighter and unsaturated (well, everything was unsaturated, it was night) mind you, it was at a place with no light pollution whatsoever.

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    Don't forget: in addition to other things going on, stars are very dim. A very dim light added to a brightly sunlit day is just not going to be very visible. A candle-flame, for example, is hard to see under sunlight.

    I think you are awesome, and I wish you the best in your endeavors, but I am tired of repeating myself, I am very busy with my new baby, and I am no longer a regular participant here, so please do not contact me to ask for advice on your career or education. All of the advice that I have to offer can already be found in the following links. Thank you.

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    ok... so what does the landscape 'fade into'? Is there fading only on the horizon?

    EDIT: when the fuck did I reach 2000?

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    It varies from place to place but where I was they were fading into dark unsaturated bluish purple.

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    Quote Originally Posted by Rhineville View Post
    . . .when the fuck did I reach 2000?
    LOL, congrats, you are officially Forum Furniture. :-)

    Now you’ve got me thinking about translucent things. Say you have some cubic tanks of different materials: a square foot of tar, a square foot of milk, a square foot of mint jell-o, a square foot of apple juice, and a square foot of water with a tiny bit of blue-gray food-coloring. That last one is the most like our atmosphere, but looking at the less transparent materials can help you better understand how light behaves when passing through substances.

    Put all the cubes in a dark room and try shining a dim flashlight (with a white light) through them. The tar would remain black because it reflects all of the light. The milk might glow whitely a bit as the light got scattered around inside of it, but you wouldn’t be able to see the light source though it. The Jell-O would glow green from light bouncing around in it, but you would probably be able to make out the vague shape of the light-source through it, strongly tinted green. The apple juice would glow slightly yellow, and the light-source would be clearly visible, if not blinding; and it would be tinted yellow. The tank of slightly-tinted water would ever-so-slightly glow with scattered light, and the light-source would be clearly visible.

    The same scenario but with the lights turned on: the tar would still be a solid cube of black. The milk would be a solid cube of white. The green-tinted light-source just might be visible through the jell-o, maybe, and there would be little or no noticeable glow. The light-source would be visible through the apple-juice, but not blindingly, and there would be no visible glow. And lastly the light-source through the water would be clearly visible, but again not as blindingly as it appeared in the dark.

    Hopefully that gives you a better idea of what the light is doing in the atmosphere. So, yes, atmospheric perspective applies just as much at night as it does during the day.

    Something else to take into consideration with landscapes: the atmosphere can extend a mile upward, but it can extend for dozens of miles toward the horizon. In fact, the higher in elevation you go, the less atmosphere is above you, and the more atmosphere is between you and the horizon. So, you could absolutely see strong atmospheric effects in the distance AND see bright stars at the same time.

    I think you are awesome, and I wish you the best in your endeavors, but I am tired of repeating myself, I am very busy with my new baby, and I am no longer a regular participant here, so please do not contact me to ask for advice on your career or education. All of the advice that I have to offer can already be found in the following links. Thank you.

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    Quote Originally Posted by Seedling View Post
    LOL, congrats, you are officially Forum Furniture. :-)
    Hooray! hehehe

    Thanks a ton for that great post too, very clearly helps me out (and duh, why didn't I think of the added distance of the atmosphere along the horizon? blah) plus has me thinking all sorts of things about light and transparency

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    There definitely is 'atmospheric fog' at night.

    There are three major components to atmosperic scattering:

    a) raleigh scattering
    b) mie scattering
    c) regular old fog

    a) Raleigh scattering is what makes the sky blue during the day. The air loves blue light, and steals some of the blue out of rays of light that pass through the air. The light that it steals is bounced around in the air, and distibuted more or less evenly.

    If you are looking at a distant light source, two things happen. 1) some of the blue light gets stolen from that light source. This is called "outscattering" 2) Some of the blue light that is scattered throughout the air is 'given back' to the ray coming from the light source. This is called "inscattering". The key here is that outscattering is proportional - for every unit of distance a ray of light travels through the air, it will lose a certain percentage of blue light. Inscattering is not proportional - for every unit of distance a ray of light travels through the air, a fixed amount of blue light will be added back to the ray.

    What this means is that bright light sources lose a net amount of blue - they lose more than they gain back from inscattering. This is why distant clouds appear a gentle yellow-orange. Dark light sources gain more blue than they lose. This is why distant, dark colored mountains become bluish. The further away it is, the more closely it's color matches the sky color.

    At night, this is still in effect. Without the sun pumping the air full of blue light, the inscattering is basically null. So at night, distant sources of light will simply be reddened. Distant lightning at night, for example, often looks orange or pink. You can sometimes see this with city lights, too.

    In photshop, this can be simulated by using an orange layer set to multipy mode, to simulate the outscattering, and a blue layer (the orange hue shfted by 180 degrees) set to screen mode to simulate the inscatter. The blue screen layer needs a depth mask. The orange multiply layer needs a special depth mask. This special depth mask would be the actual depth mask blended with the greyscale version of the image to simulate the effects of both depth and brightness. Season to taste.

    b) Mie scattering is is the tendency of the air (with dust and water droplets in it) to scatter white-yellow light. It does not scatter the light evenly in all directions, so this effect is directional and is strongest near the sun. When the sun is low to the horizon on a hazy day, the sky near the sun is a bright white-yellow.

    This wouldn't really be in effect at night, except slightly, around very bright light sources.

    The effect is purely additive, so in photoshop, screen mode works just fine so simulate this.

    c) Fog is just that. Sort of thick air. At night, this would darken distant lights.

    A layer set to normal mode, whose opacity is set with a depth mask would simulate this in photshop.

    Hope this helps.

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  11. #9
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    YVerloc, thank you, I never knew that stuff!

    I think you are awesome, and I wish you the best in your endeavors, but I am tired of repeating myself, I am very busy with my new baby, and I am no longer a regular participant here, so please do not contact me to ask for advice on your career or education. All of the advice that I have to offer can already be found in the following links. Thank you.

    Perspective 101, Concept Art 101, Games Industry info,Oil Paint info, Acrylic Paint info, my sketchbook.
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  12. #10
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    Hear that 'whooshing' sound, YVerloc? But seriously thanks, I'm defenitely bookmarking this thread. So much juicy knowledge

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